Researchers from the University of Strathclyde have helped to solve a key manufacturing challenge for next-generation optical chips used in quantum technologies, telecoms, and sensing.

The Scots scientists, in collaboration with colleagues from MIT, developed a new method for assembling the ultra-small, light-controlling devices, with their breakthrough centred on photonic crystal cavities (PhCCs), micron-scale structures that trap and manipulate light with extraordinary precision.

These are essential components for high-performance technologies, including quantum computing and photonic artificial intelligence, but until now the creation of large arrays of PhCCs has been severely limited by the tiny variations introduced during fabrication.

According to the researchers, even nanometre-scale imperfections can drastically shift each device’s optical properties, making it impossible to build arrays of identical units directly on-chip.

However, the Strathclyde-led team designed a method which can physically remove individual PhCCs from their original silicon wafer and place them onto a new chip, while precisely measuring and sorting each one by its optical characteristics in real time.

Making use of a bespoke semiconductor device integration system, designed and built at Strathclyde, researchers are able to manipulate and position these microscopic photonic devices with unprecedented accuracy, marking a major step toward scalable manufacturing.

“Using previous methods, assembling these devices felt like building a Lego set, but where you didn’t know the colour of any particular brick,” said Strathclyde’s Dr Sean Bommer, lead author of the paper.

“Now that we can measure their performance during assembly, it unlocks the potential to make more effective and complex designs.” 

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In a single session, the team successfully transferred and ordered more than one hundred PhCCs by their resonant wavelength (the specific wavelength of light that a material will absorb or transmit most strongly) creating a bespoke array they claim would be impossible to fabricate by traditional methods. 

The integration platform also allowed researchers to observe for the first time how the devices dynamically respond to the printing process, revealing elastic and plastic mechanical effects over timescales from seconds to hours.

“The ability to rearrange these microscopic devices after they have been fabricated is a crucial step in making use of them as elements in larger-scale circuits,” said Professor Michael Strain, Fraunhofer & RAEng chair in chipscale photonics.

“We’re now working towards assembling a diverse range of semiconductor devices onto a single chip to create complex, high-performance systems for telecoms, quantum applications, sensing and beyond.”